1. Don't sign up for extra texts during activation. (See update) The default SMS-add-ons are expensive and limited. If you did sign up for them then call up AT&T, cancel the add on and request this $5 all-you-can eat unlimited messaging plan instead. TUAW reader Leo signed up and reports the $5 plan is indeed iPhone compatible--at least with the postpaid (normal) phone plan. Be persistent. The AT&T rep may have to search around to find the right plan. Ask for the option that adds unlimited mobile-to-mobile text messaging for $5 per month. Read more about this option at the Howard Forums. Remember, the mobile-to-mobile texts do not include Google SMS, AIM Mobile, Facebook or any other non-cellphone texts. If you use those services, you still might get charged per message. (Update: This unlimited plan may be limited only to other AT&T phones--in which case, you may want to just sign up for the normal messaging plans.) Update 2: According to a post at the MacRumor forums, you can add both that unlimited in-network messaging and200 additional SMS msgs for $5/month.

2. You can send text messages to an iPhone by e-mail. Yeah, yeah, a lot of you already know about this. But many of our readers do not. And for you guys, here's how to do it: send your text message to phonenumber@cingularme.com (e.g. 7035551212@cingularme.com, just use the numbers, no hyphens, etc). Keep your message brief. Both the subject line and the message arrive on the iPhone.

3. It costs USD $0.15 to send and receive texts on an iPhone when using a prepaid plan. The money comes out of your account balance. If you're paying, say, 10 cents a minute, then a text would cost you one and a half minutes. Adjust the math according to your specific plan. (Mine is $0.15/minute, so one text is one minute.) This does not apply if you've added the $5/month all-you-can-eat text plan.

4. If you're on a limited prepaid plan, you'll receive a notification after each and every text. Yup, every single text you receive, every single text you send will cause the iPhone to display a message along the lines of "Your last transaction cost 0.15 USD. Your account balance is (whatever) USD". You must tap "Dismiss" every time. What a complete pain. Worse, at least in my experience, you have to dismiss this message before viewing the actual text you just received. AT&T says this is a feature, not a bug: "Your updated balance will be sent to your phone automatically after every call. you can also dial *777# at any time to see your current balance." I've tried this and it works.

5. All the Google SMS services work I'm not entirely sure why you'd want to use Google SMS but I tested it out and it certainly works. I texted fish tacos 80224 to Google and it replied with several local fish taco restaurants. Convenient when you're out of WiFi range and Safari with EDGE is responding too slowly.

6. SMS is not email SMS is limited to 160 characters per message. You can find any number of SMS FAQs via a Google search.

kthxbai Leo, Jordan Golson, and Brian Rose and everyone else who tipped us off about message features and annoyances.